The present invention pertains generally to devices and methods for use in the manufacture of balloon catheters. More particularly, the present invention pertains to devices which fold a balloon onto a catheter tube during the deflation of the balloon. The present invention particularly, though not exclusively, pertains to springs which can fold the balloon of a dilatation balloon catheter in an uniform and predictable manner during balloon deflation.
Arterial blockages caused by the build up of plaque in the arteries of a patient can have grave consequences. Specifically, the build up of plaque in arteries can reduce and eventually block blood flow through the affected vessel. When blood flow is reduced, the heart muscle is deprived of oxygen, and the patient is prone to suffer angina. In severe cases of artery blockage, the patient can suffer a heart attack.
Many modern surgical techniques have been developed to alleviate the stenoses that are formed when plaque builds up in a patient""s arteries. For example, a large number of balloon angioplasty devices exist for relieving arterial stenoses by compression of the stenosis. In several respects, balloon angioplasty devices afford numerous advantages over alternative methods. Foremost among these advantages is that open heart bypass surgery can often be avoided by using angioplasty surgical techniques to relieve stenoses in the arteries that supply blood to the heart. For obvious reasons, it is preferable to avoid open heart surgery when possible because such surgery, as is well known, is invasive and can consequently require significant post-operative recovery time. Accordingly, it is preferable to use relatively simpler angioplasty surgical procedures when such procedures are feasible. Importantly, angioplasty procedures are efficacious in the peripheral arteries as well as in the arteries that supply blood to the heart.
In angioplasty surgery, the balloon of a balloon catheter is initially attached to a catheter tube in a deflated configuration and the catheter tube connects a fluid source in fluid communication with the balloon. The balloon is then positioned at the desired location in the affected artery by advancing the catheter through the artery until the balloon is positioned next to the stenosis that is to be treated. Once the balloon has been properly positioned, fluid is infused into the balloon within the artery. As the balloon expands, it dilates the lumen of the artery and compresses the plaque. Upon being compressed, the plaque may break up or flatten out against the arterial wall. The balloon is then subsequently deflated and, once in its deflated configuration, it is either withdrawn from the artery or placed across another stenosis, to restore normal blood flow through the artery.
A particular problem associated with an angioplasty procedure exists during the deflation stage of the balloon, prior to its removal from the artery. Specifically, it is desirable that the balloon be deflated as tightly as practicable to facilitate its removal from the arterial passageways. In any case, the key to removing the balloon catheter with ease is having the balloon collapse evenly and compactly during balloon deflation. Once deflated, the balloon catheter must often travel through tortuous passageways and it is, therefore, important for the balloon to deflate uniformly into a predictable configuration. If the balloon fails to deflate in an uniform manner, an irregular bulge in the balloon may cause difficulties in withdrawing the balloon catheter from the artery.
Various techniques and balloon constructions have been developed to encourage the balloon to deflate in an uniform manner. For example, U.S. Pat. No. 5,350,361 which issued to Tsukashima et al. for an invention entitled xe2x80x9cTri-fold Balloon For Dilatation Catheter and Related Methodxe2x80x9d discloses a balloon that is constructed with tri-fold flaps. Such flaps are subjected to heat treatment so that when the balloon deflates, the same fold flaps will form allowing the balloon to return to its original deflated configuration. Another example is a balloon catheter with a means to axially twist the inflatable balloon to reduce the diameter of the balloon for passage through the artery. Such a balloon catheter is disclosed in U.S. Pat. No. 4,292,974 which issued to Fogarty et al. for an invention entitled xe2x80x9cDilatation Catheter Apparatus and Method.xe2x80x9d
There is, however, a continuing need for improved ways of deflating the balloon of a balloon catheter in a predictable manner for its removal from the artery. The present invention also recognizes the importance of collapsing a balloon evenly onto a catheter tube during balloon deflation so that the balloon catheter can be easily removed from the patient""s body without causing damage to the artery. The present invention recognizes the need for an approach that is reliable and predictable. For example, when metals (which have beneficial spring properties) are used to collapse the balloon, several factors must be considered to ensure that the resulting collapsing system is reliable. First, it is important that the metal be corrosion resistant and biocompatible. In this regard, stainless steel is corrosion resistant and has a successful history in invasive medical device applications. Nickel-Titanium alloys such as Nitinol are also suitable for invasive medical device applications.
Another important factor that must be considered when using metals is the strength and reliability of any metal joints that must be made when fabricating a metal article such as a folding spring. In greater detail, the strength and reliability of a metal joint depends on the size and configuration of the joint and the joining method. Thus, when designing a joint to be strong and reliable, it is important to maximize the surface area to be joined and to use a suitable joining method. It is also important that the joining method be easy to use and inexpensive to reduce manufacturing costs. In this regard, the present invention recognizes that soldering and spot welding, when used in conjunction with the proper joint size and configuration, are capable of producing strong reliable joints while minimizing manufacturing costs.
In light of the above, it is an object of the present invention to provide a device and method for manufacturing a device that is useful for folding a balloon predictably and compactly onto a catheter tube during balloon deflation to facilitate removal of the balloon catheter from a patient""s body. Another object of the present invention is to provide a device and method for manufacturing a device that is useful for maintaining the balloon tightly wrapped on a balloon catheter when the balloon is in a deflated configuration. It is yet another object of the present invention is to provide a folding spring for a balloon catheter having a strong and reliable metal joint to ensure the reliability of the folding spring. Yet another object of the present invention is to provide a folding spring for a balloon catheter which is relatively simple to manufacture, easy to use, and comparatively cost effective.
The present invention is directed to a device and a method for manufacturing a device for folding a balloon of a dilatation balloon catheter during balloon deflation. For the present invention, the device includes a band and a plurality of elongated fingers that are attached to the band.
Each finger in the device of the present invention has a first end and a second end, with the first end being attached to the band and the second end extending away from the band. In their extension, the fingers are substantially parallel to each other and the second end of each finger is rounded. Importantly, the device of the present invention has at least three such fingers. Further, the band of the present invention is formed with a tab and a notch and the length of the band corresponds with the diameter of the catheter tube. When the band is folded, the tab and notch are engaged with each other to form an annulus. Once engaged, the tab and notch can be bonded or soldered to each other or welded together to strengthen the joint between the tab and notch. Thus, the annulus can be considered as being centered on an axis with the fingers extending therefrom in a substantially same axial direction
In another embodiment of the present invention, the band includes a midsection and a pair of overlaps with each overlap extending from the midsection to a respective end of the band. When the band is folded into an annulus, the overlaps are juxtaposed. With this cooperation of structure, the overlaps can be joined together by soldering, welding or adhesive bonding. In a particular embodiment, each overlap is formed as a cantilever having a substantially constant thickness. In another embodiment, each overlap is formed as a tapered extension having a substantially uniform transition from the midsection to a respective band end.
The band, when it is formed as an annulus, is attached to the catheter tube of a balloon catheter by well known means, such as by using any appropriate bonding solvent. This is done with the fingers extending from the annulus over the balloon. In one embodiment of the present invention, the annulus is mounted on the catheter tube proximal to the balloon with the fingers extending in a distal direction over the balloon. Alternatively, the annulus can be mounted on the catheter tube distal to the balloon with the fingers extending in a proximal direction over the balloon. In yet another embodiment, an annulus can be mounted respectively at each end of the balloon. Importantly, in all embodiments of the present invention, the rounded ends of the fingers provide a smooth interface with the balloon to prevent them from penetrating into the balloon.
Unlike the band, which is bonded to the catheter tube, the fingers in the device of the present invention are not bonded to the balloon. Instead, they are allowed to slide on the surface of the balloon. Also, they are biased to be moved between an unstressed configuration, when the balloon is deflated and a stressed configuration, when the balloon is inflated. More specifically, in the unstressed configuration, the fingers extend at a slight angle from the annulus with an inclination toward the axis of the catheter tube. On the other hand, in the stressed configuration, the fingers are inclined away from the axis as the fingers extend over the surface of the inflated balloon.
In the manufacture of the device of the present invention, it is preferred that the band and fingers be stamped out from a single flat sheet of stainless steel. Further, prior to attaching the band onto the catheter tube, the fingers are heat treated or heat set. As a result, the fingers, when they are in their unstressed configuration, are inclined at a slight angle toward the axis to keep the balloon in its deflated configuration. Thus, whenever the balloon is deflated, the reduction of fluid pressure in the balloon during deflation will cause the fingers to return to their unstressed configuration. This causes the fingers to urge against the balloon to guide the balloon onto the catheter tube in a predictable configuration.
In the operation of the present invention, the band is first attached to the catheter tube with the fingers, in their unstressed configuration, extending over the deflated balloon. As the balloon is infused with fluid, the fingers expand away from the axis following the surface of the inflated balloon. Although the fingers will follow the expansion of the inflating balloon, the increasing stress in the fingers will cause the fingers to urge against the balloon, pressuring it to collapse back onto the catheter tube. Stated in another way, the fingers are biased in their stressed configuration to return to their unstressed configuration. Once the fluid begins to be removed from the balloon, the fingers will urge the balloon into a predetermined configuration as the fingers return to their unstressed configuration. Once the balloon is deflated and once the fingers return to their unstressed configuration, the balloon catheter may then be removed from the artery.